A physical model involving two different crystalline sites for dissolution has been developed to explain the kinetics of demineralization and remineralization of hydroxyapatite and tooth enamel. The goals of this project include correlation of the degree of demineralization of HAP crystal slurries and the sites from which it occurred to the degree of subsequent remineralization attainable with fluoride containing remineralizing solutions. In addition the kinetic properties of the dissolution sites both before and after a demineralization/remineralization treatment will be assessed. Finally, a physical model developed from these findings will be the basis for computer simulations of cycles of demineralization/remineralization of HAP pellets followed by various types of acidic attack. Results of computer simulations will be compared with experimentally accessible parameters, such as gradients of fluoride content and mineral density. The successful completion of this project would lead to greater understanding of the response of teeth to regular fluctuations in saliva composition, and would set the stage for the rational design of therapy for enhancing caries resistance.